This invention relates to pulleys and more particularly to molded plastic pulleys. One use for which the pulley of the present invention is particularly well suited is in drapery traverse rods. It will be understood that, in the context of drapery traverse rods, various special criteria are imposed. Thus, the pulley or sheave must operate smoothly, easily, and relatively silently. In addition it must be inexpensive not only with respect to its basic cost of manufacture, but also in its ease of assembly in the traverse rod. Of course, durability and maintenance-free operation are also important criteria.
Plastic materials having a wax-like surface such as Nylon, Teflon, polypropylene, polyethylene and the like are known to be suitable for molded bearings due to their respective low coefficients of friction, and although they are somewhat elastic, they are sufficiently rigid for light load conditions of this sort. On the other hand, molding bearing races out of such materials, presents certain problems which are accentuated in the drapery hardware context. Thus, if a split mold is employed a parting or "flash" line will appear on the molded article. Such a flash line can be objectionable unless great care is taken to minimize it, and the flash should not appear to any significant degree on either of the mating bearing surfaces. In the conventional practice, therefore, one procedure has been to mold smooth, completely cylindrical bearing members with the mold parting lines located along the ends of the cylinders. Thus, in one commercially available arrangement, a cylindrical sleeve serving as an inner bearing race is mounted on a pin, and the pulley is provided with an inner cylindrical bore serving as the outer race of the bearing. There are several disadvantages, however, of such a construction. In the first place, the mating cylindrical bearing surfaces provide no means for limiting axial relative motion between the pulley and the sleeve. Thus the pulley must be mounted in an outer case which keeps the pulley in the correct position on the inner race. In such an arrangement, however, the sides of the pulley rub against the walls of the pulley case, and increase both the friction and the noise. Another disadvantage is in the assembly of the various components. In one known form of such a pulley and case combination, the pulley case, the sleeve and the pulley are all made of separate molded plastic components. The pulley case is provided with opposed walls joined only at one end, and with short pins or stubs protruding from the opposed walls toward each other and in axial alignment. The pulley is assembled by pulling the walls of the pulley case apart (they being sufficiently flexible for this), snapping the sleeve onto one of the pin stubs, and then closing the pulley case so that the other stub snaps into the other end of the sleeve. Needless to say, the mold for such a pulley case is complex and expensive, and the number of parts and number of steps involved in its assembly all add to the expense. In addition, once the pulley is properly mounted in the case, additional steps are required to mount the case in one end of the traverse rod.
Accordingly, it is a general object of the present invention to provide an inexpensive molded plastic pulley which is self centering in operation and in which means are provided between the mating components of the bearing itself to restrain the bearing races against axial relative motion. Another object is to provide a pulley meeting the foregoing general object and which is also inexpensive to install in an article such as a drapery traverse rod.